Va14i NKT cells are a lymphocyte population that express an invariant Va14-Ja18 T cell antigen receptor (TCR). These cells are reactive to the CD1d (a nonclassical class I antigen presenting molecule) when CD1d binds the marine sponge-derived glycolipid a-galactosyl-ceramide (aGalCer). When activated, Va14i cells rapidly produce large amounts of IFNg and IL-4. In the proposed experiments, we will identify novel lipoglycan antigens that can stimulate Va14i NKT cells in different ways, including antagonists and antigens that alter the pattern of NKT cell cytokine production. We will determine the affinity of the interaction between the Va14i TCR and CD1 when bound to glycolipid variants and determine if the hierarchy of affinities is related to antigenic potency and cytokine profile. We will also test the physiologic consequence of differential signal strength in Va14i T cell development via antigenic challenge of mature Va14i T cells by altering the expression of fyn or Ick tyrosine kinases. The proposed experiments will provide strategies for the augmentation and regulation of this important subset of T lymphocytes.